Introduction to Bt Crops
The full form of bt is Bacillus thuringiensis. It is a bacteria that naturally produces a crystal protein that is toxic to many pest insects. These are the crops that are genetically engineered to produce the same toxin as Bt in every cell of the plant so that pests do not destroy the plant. Bt crops are often found safe because Bt is a common organic form of insecticide. When it is used by farmers it degrades within a week and sometimes just in one day. The widespread use of Bt crops, pests became bt resistance. This has become a greater threat to organic agriculture.
Types of Bt Crops
The types of Bt crops are as follows:
Bt Cotton - The cotton plant is genetically modified with the Bt gene to protect the plants from bollworm which is a major pest of cotton. Bt cotton is a transgenic crop that is an insect-resistant designed to combat the bollworm. It was created by genetically altering the cotton genome to express a microbial protein from the bacterium Bacillus thuringiensis. The genetically modified gene which has been inserted into the plant's genome produces toxin crystals that the plant would not normally produce at all. When this is ingested by a certain population of organisms it dissolves within the gut lining which leads to the organism's death.
The worms which are present on the leaves of Bt cotton become lethargic and sleepy resulting in less damage to the plants. The toxins which are produced by the crops are ingested by the pests which result in their death.
Bt Brinjal - It is also generated by the genetic transformation of a crystal protein gene cry 1 Ac from the bacterium Bacillus thuringiensis. This crop was developed to provide resistance against insects called Lepidopteron. The proteins which are produced by Bt genes bind to the receptors present on the insect's membrane which forms pores on the membranes. This damages the digestive process and leads to the death of the insect.
Bt Maize - The Bt maize was introduced to kill corn rootworm, Diabrotica virgifera which is also known as a billion-dollar bug. These crops are also derived from the Bacillus thuringiensis so the common name is Bt maize. However, this crop has revolutionized pest control in a number of countries.
About Bt
Bt is a bacterium Bacillus thuringiensis which is a family of proteins originating from strains of the bacterium Bt. To affect the different types of insects there are more than 200 different types of Bt toxins.
Basically, Bt is a spore-forming bacterium that produces crystals protein known as cry protein which is toxic to many species of insects. It is found almost everywhere in the world. It is also found in all types of terrain, including beaches, deserts, and tundra habitats. It is more significantly used in agriculture, especially in organic farming.
It is also used in organic spraying programs and in transgenic crops. Bt is used to cause mortality in pests. The toxin of Bt gets dissolved in the high pH insect gut and becomes active. The toxins which were active attack the gut cells of the insect, punching holes in the lining. The spores of Bt dribbles out of the gut and germinate in the insect causing the death of the insect within a couple of days.
Bt Gene
Bt gene is a gene that is present in the bacterium of Bacillus thuringiensis which is a soil-dwelling bacterium. It naturally produces a toxin that is fatal to certain herbivorous insects. Since 1920, it has been utilized in organic farming in the form of insecticide spray. It is also a source of the gene used to genetically modify a number of crops so that they produce the toxin on their own to destroy various insect pests. Bt genes were first used by the Belgian company Plant Genetic Systems in the year 1985 to develop genetically modified crops with insect tolerance by expressing cry genes from Bt.
1. What does 'Bt' in Bt crops stand for and what is the basic principle behind them?
The term 'Bt' stands for Bacillus thuringiensis, a naturally occurring soil bacterium. The basic principle of Bt crops involves genetic engineering. Scientists isolate a specific gene from this bacterium, known as the Cry gene, which produces a protein toxic to certain insect pests. This gene is then introduced into the crop's genome. As a result, the plant itself produces this insecticidal protein, protecting it from targeted pests that attempt to feed on it.
2. What are some common examples of Bt crops developed globally?
Several types of Bt crops have been developed to resist specific pests, enhancing crop yield and reducing pesticide use. Some prominent examples include:
3. How does a Bt crop specifically kill insect pests while remaining safe for humans and other animals?
The safety and specificity of Bt crops lie in the nature of the Bt protein. The protein produced by the plant is an inactive prototoxin. For it to become toxic, it must be ingested by an insect and enter its gut, which has a specific alkaline pH. This alkaline environment activates the toxin. The activated toxin then binds to specific receptors on the insect's midgut wall, creating pores that lead to cell breakdown and the insect's death. Since the human and most animal guts are acidic, the prototoxin is not activated and is simply digested like any other protein, posing no harm.
4. Which is the most well-known Bt crop commercially cultivated in India?
The most prominent and widely used Bt crop approved for commercial cultivation in India is Bt cotton. It was introduced to provide a robust solution against the cotton bollworm (Helicoverpa armigera), a pest that caused extensive damage to cotton yields across the country. The adoption of Bt cotton has significantly reduced the need for chemical insecticide sprays for this specific pest.
5. What are the main environmental concerns associated with the large-scale cultivation of Bt crops?
While beneficial, the widespread use of Bt crops raises some environmental concerns. The primary issue is the potential for pests to develop resistance to the Bt protein over time, rendering the crop ineffective. Another concern is the potential impact on non-target organisms, such as beneficial insects that might be inadvertently affected. Lastly, there is a risk of gene flow, where the Bt gene could cross-pollinate with wild relatives of the crop, creating unintended ecological consequences.
6. Why is genetic modification necessary instead of just spraying the Bt toxin on plants?
While *Bacillus thuringiensis* formulations can be sprayed as a biological pesticide, this method has limitations. The sprayed toxin is exposed to environmental factors like UV radiation and rain, which can degrade it quickly, requiring frequent reapplication. By integrating the Bt gene directly into the plant's DNA, the crop expresses the protective protein continuously and systemically in its tissues. This ensures that the pest ingests a lethal dose whenever it feeds on the plant, providing more consistent and effective long-term protection.
7. How do scientists ensure that a specific Bt crop targets only pests like the bollworm and not beneficial insects like honeybees?
The specificity of Bt crops is due to the highly selective nature of the Cry proteins. There are hundreds of different types of Cry proteins, and each one binds to a very specific set of receptors in the midgut of an insect. This interaction is like a lock-and-key mechanism. Pests like the bollworm have the specific 'lock' (receptor) for the Cry protein's 'key'. Beneficial insects like honeybees, as well as mammals and birds, lack these specific gut receptors. Therefore, even if they ingest the protein, it cannot bind to their gut walls and has no toxic effect.
8. What is the concept of a 'refuge' crop, and why is it critical for the long-term success of Bt technology?
A refuge is a designated area of non-Bt crops planted near a field of Bt crops. Its purpose is to manage and delay the development of pest resistance. The refuge allows a population of pests that are still susceptible to the Bt toxin to survive and reproduce. These susceptible insects then mate with any rare, resistant insects that may have emerged from the Bt field. This interbreeding dilutes the resistance gene within the overall pest population, significantly extending the lifespan and effectiveness of the Bt crop technology.